1. Technical Field
The present invention relates to a device for measuring action force of a wheel for detecting road surface frictional force, vertical drag, road surface friction coefficient, etc. which can be a constituent element of a brake system with skid control for preventing lock (seizure) of the wheels of a vehicle on sudden stops or a traction control system for preventing excessive slip of the wheels at acceleration, and a device for measuring stress of a structure for measuring stresses produced in optional structures.
2. Prior Art
The antilock brake system (ABS) of the conventional vehicle such as an automobile generally employs the principle of controlling the brake action automatically according to the chassis speed and wheel speed in such a manner that the slip ratio will fall with a certain range [cf. Japanese Patent Publication No. 59-30585 and Japanese Kokai Patent Publication No. 60-61354). The relationship between road surface friction coefficient and slip ratio is variable according to road surface condition. Therefore, in the above-mentioned system, the braking force may not be maximal depending on road surface condition and the minimum braking distance cannot be obtained in such cases. Furthermore, sicne the chassis speed is estimated from the wheel speed, control of the slip ratio is deficient in precision. Exact determination of the chassis speed requires a complicated apparatus such as a ground-relative speed sensor (cf. Japanese Kokai Patent Publication No. 63-64861), a chassis deceleration sensor (cf. Japanese Kokai Patent Publication No. 63-170157) or the like.
There was accordingly proposed an ABS which takes into account the road surface frictional force or road surface friction coefficient as a measured value. In the system described in Japanese Kokai Patent Publication No. 63-25169, the torque (tire torque) of the road surface frictional force acting on the wheels is calculated by operation from the wheel angular acceleration and brake fluid pressure and the beginning of decline in tire torque during the incremental phase of brake fluid pressure is adopted as one of the criteria for assessment of the wheel condition immediately before lock. However, in this system, the tire torque is indirectly determined by arithmetic operation from the wheel angular acceleration and bake fluid pressure but because of indefinite constants such as the wheel inertia efficiency and the braking efficiency of the brake, the precision of calculated values is not sufficiently high. Claimed to overcome the above problem, an ABS characterized by direct measurement of road surface frictional force or road surface friction coefficient has been proposed (cf. Japanese Patent Application No. 2-24819 filed by the same applicant).
Regarding the traction control system, too, the conventional apparatus detects the wheel slip at acceleration by measuring the wheel speed just as the ABS. In this case, too, there is the same problem as in the ABS wherein control is based on the wheel speed.
As constituent elements of these new ABS or traction control system, there is a demand for an apparatus for measuring dynamic quantities relating to the interaction between the road surface and the wheel such as road surface frictional force, vertical drag and road surface friction coefficient.
The object of the present invention is to meet the above demand and provide a device for measuring action force of a wheel for detecting the road surface frictional force, vertical drag and road surface friction coefficient and a structure stress measuring apparatus for measuring stresses generated in optional structures.
The present invention provides a wheel action force measuring apparatus comprising a stress detection sensor securely mounted in a hole provided in a vehicle axle through a spacer means and a signal processing circuit adapted to process a detection signal from said stress detection sensor.
In this device, the stress generated in the axle by the wheel action force is detected by the stress detection sensor installed through the spacer means. The stress is proportional to the wheel action force and, therefore, said stress detection sensor detects the wheel action force through the stress. Since the stress detection sensor is embedded in the axle, interferences to the sensor output signal from wheel action forces other than the target wheel action force can be decreased and, moreover, the sensor can be protected against the external environment. Furthermore, since the detection signal from the stress detection sensor is processed by the signal processing circuit, interferences from wheel action forces other than the specific wheel action force subjected to measurement can be further decreased.
In the above device for measuring action force of a wheel, said hole in the axle can be disposed in alignment with the stress neutral line of the axle. By so doing, said interferences to the sensor output signals from the brake torque, side force, etc. can be effectively decreased. In the above-mentioned device for measuring action force of a wheel, said stress detection sensor can be disposed on the centerline of the axle, whereby said interferences to the sensor output signal from the brake torque, side force, etc. acting on the wheel can be decreased.
Furthermore, the present invention provides a device for measuring action force of a wheel comprising a plurality of stress detection sensors independently securely embedded in a plurality of holes in a vehicle axle through respective spacer means and a signal processing circuit adapted to process a detection signal from each of said stress detection sensors to extract a specified stress. By the above arrangement, a specified action force among various wheel action forces such as road surface frictional force, vertical drag, brake torque, side force, etc. can be measured, with influences of the other action forces being decreased.
In any of the above wheel action measuring apparatuses, said detection sensor and signal processing circuit can be securely installed together in said hole in the axle. Therefore, a high signal-to-noise ratio can be achieved in the output signal from the signal processing circuit.
Furthermore, the present invention provides a device for measuring action force of a wheel comprising a stress detection sensor securely installed in each of holes formed in horizontal and vertical directions in the axle through a spacer means and a signal processing circuit adapted to process a detection signal from each of said stress detection sensors. In this arrangement, the road surface frictional force and vertical drag acting on the wheel can be measured by the stress detection sensors and the detection signal from each of the stress detection sensors can be processed in a signal processing circuit to measure the road surface friction coefficient which is defined as the ratio between road surface frictional force and vertical drag.
In any of the devices for measuring action force of a wheel mentioned above, said stress detection sensor can be constructed as an integral unit comprising strain gauges mounted on a cubic plastic base. In this arrangement, the stress detection sensors can measure the road surface frictional force and vertical drag acting on the wheel in generally the same position within the axle. Thus, the stress detection sensors can be installed in a position within the axle where interferences to the two measured values from the wheel action forces other than said wheel action forces can be simultaneously decreased.
In any of the devices for measuring action force of a wheel mentioned above, said stress detection sensor can be constructed as an integral unit comprising strain gauges mounted on a planner part at one end of a bar-shaped structure. In this arrangement, the stress detection sensor can be easily embedded in a predetermined position and in a predetermined orientation within the hole.
In any of the above devices for measuring action force of a wheel, said stress detection sensor can be constructed as an integral unit comprising strain gauges mounted on a ceramic substrate and covered up with an oxide film. In this arrangement, a highly heat-resistant stress detection sensor can be constituted.
In any of the devices for measuring action force of a wheel mentioned above, strain gauges of each of said stress detection sensors can be securely mounted in said hole in the axle in an orientation of about 45xc2x0 with respect to the horizontal and vertical stress center axes of the axle. Therefore, the respective sensors can measure the road surface frictional force and vertical drag acting on the wheel, with interferences from other wheel action forces being decreased.
Furthermore, the present invention provides a device for measuring action force of a wheel comprising an auxiliary stress detection sensor for detecting the brake torque etc. as disposed in the vicinity of a main stress sensor within a hole formed in a vehicle axle and a signal processing circuit for processing stress detection signals from these sensors to thereby eliminate or decrease brake torque and other strain signals.
The present invention further provides a device for measuring stress of a structure comprising a stress detection sensor securely mounted in a hole formed in a structure to be measured for stress through a spacer means and a signal processing circuit for processing detection signals from said stress detection sensor.
Because of this arrangement, stresses in any desired position inclusive of the interior of the structure can be measured.
In any of the devices for measuring action force of a wheel mentioned above, said signal processing circuit can be constituted of a sensor bridge circuit for stress detection and an amplification circuit. In this arrangement, interferences from wheel action forces other than a specific wheel action force can be effectively eliminated and, in addition, the sensitivity of the stress detection sensor be increased so that a sufficiently large output of the measured wheel action force can be obtained.
In any of the devices for measuring action force of a wheel mentioned above, said signal processing circuit can be constituted of a sensor bridge circuit for stress detection, an amplification circuit and an operational circuit. In this arrangement, interferences from wheel action forces other than the specific wheel action force can be effectively eliminated and the sensitivity of the stress detection sensor be increased, with the result that it is not only possible to obtain a measured value of the desired wheel action force as a sufficiently large output but also possible to determine the road surface friction coefficient which is defined as the ratio between road surface frictional force and vertical drag.
In any of the wheel action measuring devices mentioned above, said signal processing circuit can be constituted of a sensor bridge circuit for stress detection.
The effects of the present invention are as follows.
With the device according to the invention, the road surface frictional force, vertical drag, road surface friction coefficient, side force, brake torque, drive torque, etc. can be easily measured and, when the device is utilized in an antilock brake system, the braking distance can be reduced as much as possible regardless of road surface condition and, at the same time, the object of antilock can be accomplished. Moreover, there is no need for a complicated apparatus for measuring the chassis speed. In the traction control device, the acceleration distance can be reduced as much as possible regardless of road surface condition. Thus, the present invention brings forth remarkable improvements in the performance of a vehicle antilock brake system and a traction control device.
Furthermore, with the device of the present invention, any load, torque or the like can be expediently measured.
In accordance with the present invention, the technology for measuring stresses, loads or the like with a stress detection sensor equipped with strain gauges as embedded in an optional structure offers the effect that, by positioning the stress detection sensor in a suitable orientation in a hole, any desired stress, load or the like can be measured. Moreover, by placing a plurality of stress detection sensors in suitable positions and orientations, overlapping stresses or loads can be eliminated or decreased and the necessary stress or load be extracted and measured. Furthermore, this stress measuring device has an additional advantage that the stresses generated internally in an object structure can be easily measured.